On the stump, Barack Obama cites the merits of sacrifice, calling it central to patriotism and urging Americans to help change the country’s direction – whether by turning off the television so children can study or by supporting higher taxes for wealthy corporations and individuals.

Both candidates have also called for expanded national service programs and lamented the Bush administration’s failure to tap the outpouring of civic and patriotic sentiment after the 9/11 attacks.

Not since President John Kennedy urged Americans to “ask not what your country can do for you but what you can do for your country” has the rhetoric of sacrifice sat this well with the public. Concern that the US confronts a huge crisis in the form of a global financial meltdown, plus an untapped desire since 9/11 to help the nation more, makes the public more receptive to the idea that sacrifice can be noble instead of just inconvenient.

“Americans are ready to sacrifice, and they have a whole history of doing it,” says pollster John Zogby, author of “The Way We’ll Be: The Zogby Report on the Transformation of the American Dream.”

Americans have long honored the sacrifice of its warriors. During World War II, average Americans also stepped up, planting victory gardens, buying war bonds, and recycling rubbish for the war effort.

They paid more taxes, too. The Revenue Act of 1942 subjected millions to the income tax for the first time. Most seemed not to mind. In 1944, 90 percent said the amount of income tax they paid was “fair,” according to Joseph Thorndike, coauthor of “War and Taxes” and a visiting scholar at the University of Virginia in Charlottesville.

“The federal government launched an all-out campaign to market the new tax changes, including Disney-produced animated shorts featuring Donald Duck touting the importance of ‘taxes to beat the Axis!’ ” Dr. Thorndike writes in the book.

But in the past four decades, asking voters to sacrifice has been fraught with political risk. Just ask Walter Mondale. When the former vice president became the Democratic presidential nominee in 1984, the US faced a budget deficit of about $180 billion, considered massive at the time. During his nominating speech, Mr. Mondale decided to tell Americans what he believed had to be done.

“Let’s tell the truth,...” he told Democratic conventiongoers in San Francisco. “Mr. Reagan will raise taxes, and so will I. He won’t tell you. I just did.”

Previously, President Jimmy Carter hadn’t fared well either when asking for sacrifice. When the 1979 energy crisis hit, he called it a “moral equivalent of war,” famously donned a cardigan, and asked Americans to turn down their thermostats. He was not reelected.

“Sacrifice has kind of a bad name when it’s applied to the American people. We like to remember that we’ve sacrificed ... – but in terms of asking people for sacrifice, that’s the sign to a lot of people of a liberal,” says Mark Leff, a historian at the University of Illinois at Urbana-Champaign.“But the political discourse seems to be shifting.”

In his research, Mr. Zogby identifies what he calls “four meta-movements that separately and together are redefining the American dream.” Top on the list is living with limits (followed by embracing diversity, looking inward, and demanding authenticity).

If Americans are more receptive to the idea that they, personally, will be called upon to make sacrifices, it may be because the nation’s problems loom so large. The US is involved in two wars abroad and is reeling from a financial crisis, the depths of which are still unknown. More than 80 percent of Americans say the US has veered off track; to some, dangerously so. At times of crisis, historians say, citizens tend to respond to leadership that involves them in solving the problems.

“There’s some recognition of the country being under threat and being challenged and wanting to step up to it,” says Lewis Feldstein of the New Hampshire Charitable Foundation. “Obama is responding and generating and evoking this. I also feel there’s some of that in McCain’s rhetoric as well, with his ‘Country First’ [motto].”

Obama often invokes the “decent, generous” nature of Americans and their willingness to “sacrifice for future generations.”

“Patriotism must, if it is to mean anything, involve the willingness to sacrifice – to give up something we value on behalf of a larger cause,” he said in Florida in June.

When introducing McCain, his wife, Cindy, often praises his history of “sacrifice and service” as a prisoner of war and refers to him as “the man who taught me about selfless sacrifice.” At a September event in New York on the importance of national service, McCain explained his views this way:

“The best way to commemorate and to show our appreciation – and love and sympathy for the families of those who’ve sacrificed – is to serve our country....”

A key to public acceptance is how sacrifice is characterized. Mr. Carter’s initial calls to sacrifice were successful, Zogby argues. “We did put sweaters on, and we did turn our thermostats down. But then he turned it into a malaise and blamed the victim, which didn’t cut it.”

Americans have been cranky about high gasoline prices this summer and Congress’s vote to spend billions to bail out troubled banks. But the credit crunch, plummeting stock market, and risk of severe recession have been sobering. “Now somebody has to connect it and say, ‘There’s more sacrifice to come, but now it’s for something better – a better nation,’ ” Zogby says.

Of the two candidates, some analysts say, Obama has been more effective in evoking sacrifice than has McCain, who relies on his own history to stand as an example in itself.

“Obama’s goal is to look more like Franklin Roosevelt,” says Darrell West, director of governance at the Brookings Institution, a Washington think tank. “We faced a real challenge in the 1930s, and people ... were willing to sacrifice because they knew the future of the country depended on it.

Obama has to basically say, ‘We’re facing a crisis on the level of the Great Depression, and we’re going to have to make sacrifices if we’re going to solve this.’ ”

When McCain talks about sacrifice, it’s usually in terms of national security. He has also said a “call to serve” will be central to his administration. But on the campaign trail, the Republican candidate has shied away from asking average people to sacrifice directly. Some analysts see his attack on Obama for “redistributing the wealth” as a kind of code for “Obama will ask you to sacrifice your money” – something that has never played well politically.

“What McCain’s doing is saying, ‘You mean that anybody is supposed to give anything up for anything else? That’s not what we do,’ ” says Professor Leff. “Sacrifice is OK and absolutely legit if you’re talking about soldiers, but that’s it.”

Whichever candidate is elected Tuesday, levels of public involvement in the campaign so far and high voter turnout could indicate a fundamental change in American political discourse and expectations.

“We may be on the verge of a substantial shift in ... the political dialogue and rhetoric that dominate American politics,” says Dr. Thorndike, the “War and Taxes” coauthor, in an interview. “We have a real crisis right now that presents an opening for someone who knows how to rally the country in pursuit of a common objective.”